Conventionally, a wireless communication system operates in a proprietary radio frequency (RF) spectrum in which base stations and wireless terminals communicate through the proprietary RF spectrum licensed to a wireless operator. However, there have discussions of wireless communication systems expanding usages to unlicensed spectrum, such as the Industrial, Scientific and Medical RF spectrum (ISM band) or other free spectrum. The possibilities of Long Term Evolution (LTE) or LTE-advanced communication systems making incursions into the unlicensed spectrums have drawn attention for telecommunication equipment vendors and operators. This has been known as ‘Licensed Assisted Access (LAA)’. Currently, there has been endeavors to for attain a single global solution framework for Licensed Assisted Access (LAA) to unlicensed spectrum. One reason for such interest is the potential overcrowding of licensed spectrums. In order to provide high throughput services to more users, incursions into unlicensed spectrums might alleviate overcrowding of for wireless communication systems. However, such efforts would require solutions for numerous difficulties.
The unlicensed spectrum has been considered by cellular operators more and more as a complementary radio resource to augment their services. According to 3GPP TR 36.889 and RP-141664, LAA could be considered a secondary component (CC) carrier integrated into LTE. However, high priority should be on the completion of the DL only scenario.
Unlike LTE for which an operator would possess a specific set of operation channels, an unlicensed spectrum would need to be shared and could be shared by almost any access technologies for wireless communications. One who initiates a communication on an unlicensed spectrum may need to undergo a contention phase in order to use the frequency of unlicensed spectrum. The winner of the contention would possess the right to communicate on the frequency for a limited period at a time as defined by regional regulations such as 4 ms for each occupancy in Japan and 10 ms for each occupancy in parts of Europe. Hence, the availability of unlicensed spectrum is uncertain when one intends to communicate on the spectrum. The coverage of LAA nodes operating on unlicensed spectrum may range from 50 m to 100 m for the 5 GHz spectrum.